The present invention relates generally to a dual unvented sealing system and, more particularly, to a sealing system having primary and secondary seals wherein the primary seal can release the interstage pressure when system pressure is reduced.
In many applications of hydraulic systems, such as in modern aircraft, there is a need to be able to manually extend and retract the rod connected to an actuator. Because of the new composite designs of aircraft bodies, when repairs are to be accomplished, one cannot jump up and down on the flight control surfaces to connect the flight control surfaces to the actuators. One has to be able to manually move the actuator to the control surface. Interstage pressure buildup or trapping between dual unvented seals of the actuator, prevents easy manual reversal of the actuator rod because the seals remain energized.
Prior solutions to solving this pressure buildup problem between the two seals involved providing one of the seals with two backup rings that shift within the seal gland. In this case, the groove or gland in which the seal sits allows the seal to move back and forth axially upon the rod. It was believed that, upon system pressure reduction, the seals would move within the glands away from the interstage pressure volume thus creating a larger volume for the pressurized fluid between the two seals, whereby the increased volume would act to reduce the interstage pressure. However, in practice the pressure did not drop enough to solve the problem.
Another attempt to solve the problem was by putting a pressure relieving notch in the elastomer and to provide narrow backup rings. This construction did not consistently relieve interstage pressure at all times, since the backup ring itself could act to seal within the rod bore glands.
Another problem of prior art dual sealing systems was seal extrusion with a sufficient temperature increase of the interstage volume.
The present invention is directed to overcoming the aforementioned problems associated with dual unvented seal systems, wherein it is desired to provide a primary seal permitting reliable pressure relief of the interstage area between the primary and secondary seals, to allow manual movement of the actuator rod or piston.